Conjunct polymers are common by-products of acid-catalyzed alkylation reactions including the alkylations of isoparaffins, e.g. isobutane and isopentane, with light olefins, e.g. propylene and butenes, to produce high octane and clean burning alkylate gasoline. The term conjunct polymer was first used by Pines and Ipatieff to distinguish these polymeric molecules from typical polymers. Unlike typical polymers which are compounds formed from repeating unites of smaller molecules by controlled or semi-controlled polymerizations, “conjunct polymers” are “pseudo-polymeric” compounds formed asymmetrically from two or more reacting units by concurrent acid-catalyzed transformations including polymerization, alkylation, cyclization, additions, eliminations and hydride transfer reactions. Consequently, the produced “pseudo-polymeric” may include a large number of compounds with varying structures and substitution patterns. The skeletal structures of “conjunct polymers”, therefore, range from the very simple linear molecules to very complex multi-feature molecules.
Some examples of the likely polymeric species were reported by Miron et al. (Journal of Chemical and Engineering Data, 1963) and Pines (Chem. Tech, 1982). Conjunct polymers are also commonly known to those in the refining industry as “red oils” due to their reddish-amber color or “acid-soluble oils” due to their high uptake in the catalyst phase where paraffinic products and hydrocarbons with low olefinicity and low functional groups are usually immiscible in the catalyst phase. In this application, the term “conjunct polymers” also includes ASOs (acid-soluble-oils) red oils and C12+ polyalkylates.
Separating conjunct polymers formed as by-products during HF-catalyzed isoparaffin/olefin alkylation from the catalyst-alkylation products-conjunct polymer mixture has been described in U.S. Pat. No. 5,382,746.